1. Field of the Invention
The invention relates to a radio frequency identification (RFID) system, and more particularly to a radio frequency identification system comprising a passive tag.
2. Description of the Related Art
Radio frequency identification (RFID) utilizes a wireless method to transmit data and to obtain the related information of a tag. The tag is disposed in an object, for identification. When the object enters the read range of a reader, the tag issues some information, such as identification (ID). The reader receives and decodes the information. The decoded result provided by the reader is transmitted to a behind computer. After the behind computer processes the decoded information, the identifying procedure is finished.
For a passive tag, the reader provides the required power to the passive tag. However, the power provided by the reader is dependent upon the distance between the reader and the passive tag. For example, when the distance between the reader and the passive tag is longer, the power received by the passive tag is reduced. When the power received by the passive tag is insufficient, the passive tag cannot transmit information to the reader.